The present invention relates to a tandem master cylinder for hydraulic brake systems of automotive vehicles, comprising a housing in whose longitudinal bore a first and a second piston are sealedly slidably guided and confine a first and a second pressure chamber which are in communication with a supply reservoir by two central valves which open in their release position. A resetting spring is provided which preloads the first piston and is arranged outside of the longitudinal bore. The first central valve is placed in the second piston and the second central valve is arranged at the end of the longitudinal bore separately of the second piston.
A tandem master cylinder of this type is disclosed in German patent application P 37 17 706.0. A particular characteristic of this tandem master cylinder, which is preferably used on slip-controlled brake systems and the central valves of which are designed as regulating valves, is that the two working pistons (primary and secondary pistons) are separated from each other and cooperate with stationary stops, with the first central regulating valve being placed in the secondary piston and the second central valve being arranged at the end of the longitudinal bore of the master cylinder housing separately of the secondary piston.
It is a shortcoming in this known tandem master cylinder that the axial length of the second (secondary) pressure chamber must be dimensioned so as to allow the accommodation of a piston-resetting spring. Therefore a short tandem master cylinder construction is not possible.